Fuel pump for injectors



Oct. 26, 1937. A. FIELDEN FUEL PUMP FOR INJECTQRS 2 Sheets-Sheet 1 FiledNov. 28, 1934 Oct. 26, 1937. A. FIELDEN FUEL PUMP FOR INJECTORS FiledNov. 28, 1934 2 sheets sheet 2 Patented Oct. 26, 1937 UNITED STATES FUELPUMP FOR INJECTORS Arthur Fielden, Detroit, Mich., assignor to GeneralMotors Corporation, Detroit, Mich, a corporation ,of DelawareApplication November 28, 1934, Serial No. 755,157

25 Claims.

This invention relates to pumps and especially toplunger pumps 'forintermittent delivery of fluid through a pressure loaded delivery valveduring the middle portion only of the discharge stroke of the plunger,the beginning and ending of each discharge stroke being made ineffectivefor delivery through the loaded delivery valve by the opening ofsuitable bypass or relief ports providing an alternative path for theflow of fluid from the pump pressure space during these portions of eachdischarge stroke.

It relates particularly to injection pumps for the supply of fuel to aninternal combustion enr gine in which the pressure loaded delivery valvemay constitute an injection valve.

Such an injection-pump in one unit with an injector, is shown in U. S.Patent No. 1,981,913,

wherein a part of the charge in the pump pressure space is rejectedtherefrom, through bypass 20 or relief ports controlled by the pumpplunger, into a single annular chamber surrounding the plunger cylinderbarrel and forming a reservoir, constituting a part'of the supply lineto the pump, for fuel at low pressure from a suitable source. 25Rejection of fuel into this supply line takes place before and after thedelivery of a variable measured quantity of fuel at high pressurethrough the loaded delivery valve. An air cushion chamher. or any othersuitable form of resilient storing 30 space suflicient to hold thevolume of fuel rejected on any discharge stroke and to form a resilientcushion for the pressure surges in the supply line, is provided incommunication with the uppermost part of the reservoir. The fuelrejected before delivery through the loaded delivery valve is rejectedfrom the uppermost part of the pump pressure space, thereby eliminatingalong with the rejected fuel any air or gas bubbles which will rise tothe uppermost part 'of the pressure space, before delivery takes place,the pump plunger moving downwardly on its delivery stroke for theinjection of fuel downwardly into an engine cylinder. The pump plungeris 45 provided'with helical control edges whereby the time and quantityof fuel delivered may be varied'in known manner by a turning adjustmentof the plunger.

The present invention relates to improvements 50 in the unit fuel pumpand injector shown in Patent No. 1,981,913 and to a modificationenabling the functional results of the structure shown in Patent No.1,981,913 to be obtained in those cases where the assembly is inverted55 for the injection of fuel upwardly into an engine cylinder, theplunger moving upwardly on its delivery stroke.. I V

One object of the invention is a fuel pump of the kind described inwhich the amount of fuel bypassed before delivery through the loaded de-5 livery valve is constant, or alternatively, directly proportional tothe amount delivered through the loaded delivery valve.

Another object of the invention is a fuel pump of the kind describedhaving positive valve venting means open through a certain period of thecycle of operation of the pumpto relieve the reservoir of any excess airor gas bubbles.

' Another object of the invention is to provide for a through flowscavenging of the reservoir at the fuelsupply pressure.

A further object of the invention is to provide for air venting of thereservoir at a pressure higher than the fuel supply pressure.

A still further object of the invention is a modification of thestructure of the unit fuel pump and injector of U. S. Patent No.1,981,913 adapted for operation in a relatively inverted position forupward injection of fuel and having the foregoing objects of theinvention applied thereto.

The above and other objects of the invention will be apparent as thedescription proceeds.

According-to the invention, that control edge on the pump plunger whichcontrols the closure with the latter arrangement, the degree ofpreliminary bypassing may be proportional to the quantity delivered.

The venting of the reservoir both for the elimination of air from thesystem and for any desired amount of "through flow scavenging iseffected tive valve means for venting the reservoir for the eliminationof undesired air in the system enables this elimination to be positivelyeffected with a minimum of through flow of fuel, thus reducing thequantity of fuel to be recirculated through the low pressure supplysystem and hence avoiding any infiltration of additional air in the fuelso recirculated.

The velocity of air or gas at a certain pressure through an orificebeing several times greater than the velocity of a liquid at the samepressure through the same orifice, the bore of the vent and the timewhich it remains open can be made such that all undesired air or gas canbe eliminated from the reservoir, while only a comparatively smallamount of liquid fuel can escape through the vent in the samecircumstances.

By suitably disposing on the pump plunger the control edge or edges forthe vent port, the reservoir may be vented either before the beginningof the discharge stroke at the supply pump pressure, or after the end ofthe discharge stroke at a pressure higher than the supply pump pressure,in a manner later to be described.

The accompanying drawings show the application of the invention to afuel pump of the kind described arranged for upward injection andalternatively for downward injection of fuel.

In the drawings:

Figure 1 shows in part sectional elevation, a

combined fuel pump and injection nozzle of the kind described, mountedin the cylinder head of an internal combustion engine and dischargingupwardly thereinto.

Figure la is an enlarged view of a part of Figure 1 showing theinjection nozzle.

Figure 2 is a perspective view of a suitabl check valve for the bypassport to prevent the influx of fuel'into the cylinder barrel through thisport.

Figure 3 is a section on line 3--3 of Figure 1 showing the means forangular turning adjustment of the plunger, to vary the time and quantitydelivered through the loadedv delivery valve.

Figure 4 is a section on line 4-4 of Figure 1.

Figure 5 is a section on line 55 of Figure 1, showing the means oflocating the cylinder bushing in the pump housing and the ducts fordraining excess air and fuel leakage away from the injector.

Figure 6 is an enlarged perspective view of the end of the pump plungershowing a control edge for the closure of the inlet port providing for aconstant interval between closure of the inletport and closure of thepreliminary bypass port as shown in Figures 7, 9 and 10.

Figure 7 shows a fuel pump similar to Figure 1, but having a plungercontrolled port 'for the air venting and pressure relief of thereservoir, and a combined check valve and safety valve in the supplyline.

Figure 8 is-an enlarged section on line 8-8 of Fig. '7.

Figure 9 shows a fuel pump for use with injectors dischargingdownwardly, having "a plunger controlled port for the air venting andpressure relief of the-reservoir, and a combined check" valve and safetyvalve in the supply line.

Figure 10 shows a modification of Figure 9 with .means for opening theport for the air venting and pressure relief of the reservoir at the endof the discharge stroke of the pump plunger.

Figure 11 shows a similar modification of Figure 7.

Figure 12 is an enlarged view of a part of Figbushirig in the housing I.

" pocket 20 for a spring 2|.

edge I. An annular groove or space 2 divides the circumferential surfaceof the plunger into two parts. The annular groove isbounded by a helicaledge 3 and a helical edge 4.

The plunger works in a cylinder 8 which is a Between the bushing and thehousing is an annular chamber 8 formed by an enlarged bore of thehousing. Two ports 9 and Illthrough the wall of the bushing 6 connectthe annular chamber 8 with the bore of the bushing.

A duct drilled through the housing into the end of the annular chamber 8serves for the supply of fuel to this annular chamber from any suitablelow pressure source.

The housing is counterbored to form a pocket l3 for a pinion |4 having abearing formed by a boss I5 extending into the bore of the housing andhaving a clearance between itself and the end of the bushing to providea space Hi therebetween.

The plungerl has a' hexagonal spline portion l! in the pinion I4 so thatit may be turned thereby, but is capable of longitudinal reciprocatingmotion therein. The pinion l4 may be angularly turned for adjustment ofthe beginning and end of injection by a rack I8 which can slide back andforth in a horizontal groove IS in the housing, opening out into thepocket IS. The rack is retained in the groove by a plate l9.

The housing I is counterbored to provide a The outer end of the plungeris provided with a head 22 and a seating collar 23 for the spring 2|.The other end of the spring is provided with a seating collar 24 bearingagainst the end of the pocket 26.

The outer end of the plunger with its spring is enclosed by a cover 25,which reciprocates in the pocket 20 under the influence of any suitabledriving means. As shown,the plunger is actuated on its discharge stroke,through the medium of a rocking lever 26 with rollers 26 and 26", by acam 21, the spring 2| effecting the return or suction stroke of theplunger.

The end of the housing 1 is internally threaded for the injection valveparts, consisting of a nozzle piece 28, a valve seat piece 29, and,adistance piece 30 constituting a spring .housing, .all within a boredout threaded cap piece 3|, which screws into the housing. 7

The nozzle piece 28 has a conical seating in the cap piece 3|, and allthree parts 28, 29 and 38, together with the bushing-6, are clampedtightly together and onto a shoulder 32 in the housing I, when the cappiece 3| is screwed therein, leaving a clearance space 33 between thebushing and the cap piece 3|.

A duct or ducts 34 through the piece 30 lead the fuel from the pumppressure space to a duct or ducts 36, leading to a chamber 31 in thepiece 29. In this chamber 31 is a seating for an 111-- collar 44 on astem piece 45 for the valve which I predetermined amount.

The strength of the spring 43 and the loading it provides for theinjection valve 38 which is the loaded delivery valve of the pumpdetermines the minimum injection pressure.

The port It! is provided with a check valve of any suitable type. In theexample illustrated, it consists of a fiat spring 48 curved to fittightly in a shallow annular groove 49 around the bushing 6, with oneend over the port I and the other end locating and holding the spring inposition by a projection or dimple 50 formed thereon, and sprung into acorresponding depression in the bushing.

The bushing 6 is located in the housing I with its ports 9 and I0 at'anormal definite angular relationship to the housing by a pin 52 (seeFigure 5).

A small screw 53 through the housing 1 engages a slot 54 in the cover25, retaining the cover over the plunger and its spring, but permittingits reciprocating movement.

The complete assembly constitutes a unit fuel pump and injection nozzlewhich may be mounted in a suitable bore through the cylinder head of aninternal combustion engine.

As shown, the cap piece 3| of the combined fuel pump and injectionnozzle has a conical seating in a bore through a'cylinder head 55 inwhich it is held by-the studs 56. A-suitable clearance between this boreand the housing! provides an annular space 51 into which all leakage andventage from the pump may collect.

The clearance space I5 is connected to the annular space 51 by a port46'inFigures 1, 5, '7 and 11 and by a port 46 in Figures 9 and 10.

Leakage and excess fuel is returned from the? annular space 51 to asupply tank (not shown) through a duct 58' in the injector housing inFigures 1, '5, 7 and 11, and with the construction according to Figures9 and through a duct 58 in tween the pressure space and the annulargroove.

The flanged end 60 of the cylinder barrel 6 which is clamped onto theshoulder 32 of the housing 1 has its periphery grooved by channels 6|which connect the reservoir 8 with the clearance space 33 whichconstitutes an air cushion chamber.

In Figure 1 a leakage path for air in excess of that required to fillthe chamber 33 is provided by a fitting of the parts such that there isa slight clearance between the periphery of the flange 68 and thehousing. I, and air which leaks therebetween'from the cushion chamber 33passes to the outside of the housing through a drain hole 62. 1 v

The operation of the construction for upward injection of the fuelaccording to Figure 1, is as follows: fuel at a small head of pressureis supplied to the annular chamber 8 through the duct II. In theposition shown, the plunger lis at the end of its suction stroke and hasuncovered the inlet port 9, allowing oil to fiow into the pumping space.As the plunger is'moved inwards on its discharge stroke, it first coversthe inlet port 9 and then pumps oil and any gas bubbles the fuel in thereservoir.

mixed therewith out from the uppermost part of the pumping space 5'through the duct 5' into the annular space 2 and out through the bypassport l0 back into the annular chamber 8 until the edge 4 covers the portl0. At this point, and there now being no other outlet from the pumpingspace, the pressure rises rapidly in the pumping space and itsconnections with the chamber 31 containing the spring loaded valve 33,until voir 8. The air chamber 33 acts as a. pressure accumulator,reducing the pressure variations on the inlet side of the pump as aresult of the opening and closing of the ports 9 and Il Excess air inthe airchamber 33 escapes at any time through the port 62, by virtue ofthe clearances provided.

It will be noted that in the construction according to Figure 1, theedge I of the plunger, which controls the closure of the inlet port 9 iscut square with its axis, and therefore if thetime of closing of thebypass port ID by the helical edge 4 is advanced by a turning adjustmentof the plunger, the quantity bypassed before the beginning of injectionwill be lessened'while the quantity injected is increased, and viceversa.

In order to ensure the elimination of air and gas bubbles from the pumppressure space along with the volume bypassed before the beginning ofinjection 'it is desirable that this bypassed volume should be at leastconstant or directly proportional to the amdunt of fuel deliveredthrough the injector and not lessened when the quantity injected isincreased.

Referring now to Figure 6, it will be noted that the edge I of theplurfger--which is the control edge for the closure of the inlet port 9--is helical and of the same pitch as the helical edge 4 which controlsthe closure of the bypass port l8; 1. e. it has the same lead or advanceas the helical edge 4, and therefore if in the plunger stroke the timeof closing of the bypass port is advanced or retarded by a turningadjustment of the plunger, the time of closing of the inlet port will beadvanced or retarded to a like extent, and the distance moved through bythe'pump plunger between closure of the inlet port and closure of thebypass port will be constant; hence the volume bypassed through thebypass port I0 before the beginning of in? ction will be invariable.

If the pitch of the helical edge .I is increased to the proper degreegreater than the pitch of the helical edge 4, the inlet port 9 will beclosed earlier as the bypass port I8 is closed earlier, and

- the volume bypassed through the bypass port M before the beginning ofinjectionmay be made directly proportional to the amount of fueldelivered through the injector.

I In Figures '7 and 11, air or vapor separating out from the fuel inexcess of that requiredto fill the cushion chamber 33 is displaced fromthe reservoir 8 through a duct 61 by the pressure of In Figure '7 thisventing of the reservoir takes place along with a through flow of thefuel, during the dwelP' period provided by a dwell portion on the cam21, between suction and discharge strokes of the pump, there being anannular groove 68 around the plunger which during this period puts theduct 61 in communication with a port 68 in the bushing, leading to theannular space 51 through a coincidental port 10 in the housing. InFigure 11, the venting of the reservoir takes place at the end of thedischargestroke of the pump plunger, the plunger having a portion ofreduced diameter bounded by an edge 12, which, at the end of thedischarge stroke, puts the vent duct 61 in communication with theclearance space i6 which is connected with the annular space 51 and thedrain duct 58' by the port 46'.

The operation of the constructions for downward injection of the fuelaccord ng to Figures 9 and 10, is, in its essentials, functionallyidentical with that of the constructions according to Figures 7 and 11,respectively. In Figures 9 and 10 the pressure space in front of theplunger and the annular groove 2 are in= communication with each otherat all times through the groove 5 in the plunger. On the closing of theinlet port, oil and any gas bubbles mixed therewith are pumped outthrough the bypass port i8 directly from the annular space 2. A bore l2extending upwards from the upper end of the annular reservoir chamber 8and having its outer end closed by a screwed plug !2' constitutesthe'air cushion chamber. The end of the bushing 5 away from theinjection valve is a. tight fit in the housing 1. Airor vapor separatingout from the fuel in excess of that required to fill the cushion chamberI2 is displaced from the reservoir 8 through a port 63 by thexpre'ssureof the fuel therein. In Figure 9-this venting of the reservoir takesplace along with a through flow" of the fuel during the dwell periodbetween suction and discharge strokes of the pump, there being anannular groove 64 around the plunger which, during this period, puts theport 68 in communication with a drilled hole 65 in the bushing 6,leading to the clearance space l6 and thence throughthe port 46 into theannular space 51. In Figure 10 the venting of the reservoir occurs atthe end of the discharge stroke of the pump plunger, the plunger havinga portion of reduced diameter bounded by an edge 13 which, as theplunger approaches the end of its discharge stroke, puts the vent port63 in communication with the clearance space l6 which communicatesthrough a port 46 with the annular space 51.

The arrangements according to Figures '7, 9,

10 and 11 having valved venting of the reservoir, 8 are preferablyprovided with a combined nonlar passage through which, when the member14 is oil its seating, fluid may flow through radial grooves such as inthe end of the pipeunion, into the supply pipe 18-.

Within the valve member valve 8| yieldingiy urged onto its seating 82therein at that end thereof remote from the seating 1rby-aspringr83llhesprings 83 and 11 are respectively such that fluid can flow throughthe ball check valve 8| into the duct I i and reservoir 8 u is a ballcheck from the supply pipe 18 whenever the pressure therein is less thanthe supply pressure, and can flow through the safety valve 14 out fromthe reservoir 8 and duct II when the pressure therein is greater thanthe supply pressure to an extent governed by the pressure of spring 11.

With such a non-return and safety valve in the supply line, the pressurein the annular reservoir 8 will rise during the period of preliminarybypassing and again upon the opening of port 8 to terminate injection toa pressure higher than the supply pressure, but not greater than amaximum, controlled by the spring loading of safety valve 14 which is,of course, arranged to open at so ne suitable pressure lower than thepressure required to lift the injection valve or: its seat. In this wayan intermediate pressure stage between supply pressure and injectionpressure will be built up in the'reservoir 8 in every cycle of the pumpplunger.

In the constructions according to Figures 7 and 9, this intermediatepressure, higher than the supply pressure, will be effective to rechargethe pumping space on the suction stroke until the pressure in thereservoir 8 falls to supply pressure, when the non-return ball checkvalve 8| will open the reservoir to the source of supply. A more rapidfilling of the pump pressure space is thus obtained, which isadvantageous in a pump working at high speed.

In the modifications according to Figures 10 and 11, the intermediatepressure will be relieved by the opening of the vent port 68 and thevent stroke, whereby the reservoir is vented at a pressure higher thanthe supply pressure.

In all the arrangements according to Figures 7,9, 10 and 11 and providedwith a non-return and safety valve as described in addition to theforegoing and to the fact that high pressure surges will not normally betransmitted to the supply line, the intermediate pressure stage built upin the reservoir on each discharge stroke will be eflective to reduceleakage between the plunger and the cylinder barrel by reducing thepressure difference on the inside and outside of the cylinder barrel andthus reducing the stresses safety valve- -less than the pressurerequired to hold theinjection valve ofl." its seat.. While,

however, the reservoir has been shown with such an air chamber space toconstitute a resilient capacity expansible under pressure, the inventionis not limited to such a specific means of ab- 1. A fluid pumpcomprising a cylinder, 9.

plunger in the cylinder, the said plunger moving upwardly on itsdischarge stroke and delivering fluid upwardly through an upwardlydirected delivery outlet, an inlet port and 'a bypass port in thecylinder, the bypass port being lowermost and axially spaced from theinlet port, the delivery outlet being above the inlet port but below theuppermost part of the pump pressure space, control edges for the portsconstituted by the end of the plunger and the two edges of an annulargroove therein, a duct connecting the uppermost part of the pumpcylinder pressure space with the annular groove in all positions of theplunger in which either the inlet port or the bypass port is open to theannular-groove, and forming the only connection between the pumppressure space and the annular groove, all whereby, on the dischargestroke of the pump, the bypass port is open after the inlet port hasclosed and a part of the pump charge including any air or gas bubbles isexpelled through the bypass port from the uppermost part of the pumpcylinder pressure space after the closure of the' inlet port and beforedischarge through the delivery outlet consequent upon closure of thebypass port.

. 2. In a fluid pump having a cylinder, a plunger cooperative therewithas a pump for the pressure discharge of a predetermined quantity offluid through a delivery outlet, coacting ports and control edgestherefor on the cylinder and plunger, respectively, including an inletport and a bypass port whereby fluid is bypassed out from the cylinderafter the closing of the inlet port and before the pressure dischargethrough the delivery outlet, the control edges for closing the inlet andbypass ports being inclined and so arranged that Y upon a relativeadjustment of the cylinder and plunger the inlet port is closed earlieras the bypass port is closed earlier, the inclination of the controledge for closing the inlet port being not less than the inclination ofthe control edge for closing the bypass port, whereby the quantitybypassed before discharge through the delivery outlet is not lessened asthe bypass port is closed earlier. 7

. 3. In a fluid pump having a cylinder, a plunger cooperative therewithas a pump for the pressure discharge of a predetermined quantity offluid through a delivery outlet, coacting ports and conrespectively,including an inlet port and a bypass port whereby fluid is bypassed outfrom the cylinder after the closing of the inlet port and before thepressure'discharge through .the dethe quantity bypassed before dischargethroughthe delivery outlet remains constant irrespective of the time ofclosing of the bypass port.

4. In a fluid pump having a cylinder, a plunger cooperative therewith asa pump for the pressure discharge of a predetermined quantity of fluidthrough a delivery outlet, coacting ports and control edges therefor onthe cylinder and plunger, respectively, including an inlet port and abypass port whereby fluid is bypassed out from the the inclination ofthe control edge for closing the bypass port, whereby the quantitybypassed before discharge through the delivery outlet is increased asthe bypass port is closed earlier.

5. In a fluid pump having a cylinder, at plunger cooperative therewithas a pump: for the pressure discharge of a predetermined quantity offluid through a delivery outlet, coacting ports and control edgestherefor on the cylinder and plunger respectively including an inletport and a bypass port whereby fluid is bypassed out from the cylinderafter the closing of the inlet port and before the pressure dischargethrough the delivery outlet, the control edge for closing the bypassport being inclined so that the time of closing of the bypass port isvariable by a relative adjustment of the cylinder and"plunger, thequantity delivered being increased as the bypass port is closed earlier,the control edge for closing the inlet port being inclined and soarranged that the inlet port is closed earlier as the bypass portisclosed earlier, said lastnamed control edge having an inclination notless than the inclination of the controledge for closing the bypass portwhereby the quantity bypassed before discharge through the deliveryoutlet is not lessened as the quantity delivered is increased. t

6. The combination according to claim 5 in which the control edge forclosing the inlet port has an inclination equal to that of the controledge for closing the bypass port, whereby the quantity bypassed beforedischarge through the trol edges therefor on the cylinder and plunger,

cylinder after the'closing of the inlet port and before the pressuredischarge through the delivery outlet, the control edges for closing theinlet and bypass ports being inclined and so arranged that upon arelative adjustment of the cylinder and plunger the inlet port is closedearlier as thebypass port is closed earlier, the inclination of thecontrol edge for closing the inlet port being greater than I deliveryoutlet-remains constant as the quantity delivered is increased.

'1. The combination according to claim 5 mwhich the control edge forclosing the inlet port has an inclination greater than that of thecontrol edge for closing the bypass port, whereby the quantity bypassedbefore discharge through the delivery outlet is increased as thequantity delivered is increased. g

8.- In a fluid pump comprising a cylinder and a plunger cooperativetherewith as a pump, a delivery outlet for the pressure discharge of apart only of the volume of fluid displaced by the pump, a. reservoir forfluid under pressure forming part of the supply line to the pump from alow'pressure source of supply, inlet and bypass valve means between thepump pressure space and the reservoir, and means for venting thereservoir including suitable passageways independent of the pumppressure space,- having valve means constituted by a port and a coactingcontrol edge therefor on the cylinder and plunger respectively.

9. A fluid pump according to claim 8, in which fluid including any gasbubbles is bypassed from the'pump into the reservoir after the closingo'fithe inlet valve and before the beginning of discharge through thedelivery outlet.

10. A fluid pump according to claim 8, having a non-return valve in thesupply line to the reservoir. i g

11. A fluid pump according to claim 8, having a non-return and safetyvalve in the supply line to the reservoir.

i 12. In a fluid pump comprising a cylinder and part only of the volumeof fluid displaced by the pump, a reservoir for fluid under pressureforming part of the supply line tothe pump from a low pressure source ofsupply, inlet and bypass-.

valve means between the pump pressure space and the reservoir, saidinlet and bypass valve means being constituted by ports and coactingcontrol edge therefor on the cylinder and plunger respectively, andvalve venting means for the reservoir constituted by an additional portand coacting control edge therefor on the cylinder and plungerrespectively.

13. A fluid pump according to claim' 12, in-

which the valve venting means, opens from the reservoir at a pointhigherthan the inlet and bypass valves open thereinto.

14. Ina fluid pump in, combination, a cylinder,

.a bypass port, both adapted to provide a path of flow between the pumppressure space and the reservoir, the bypass port opening from thatpartof the pressure space which is uppermost at a pointhigher than the inletport and the said delivery outlet, whereby fluid and any air or gasbubbles in the cylinder are bypassed out from the uppermost partthereof, into the reservoir, after the closing of the inlet port andbefore pressure discharge through the loaded delivery valve, and meansfor venting the reservoir at a point higher than the inlet and bypassports open thereinto, to relieve the reservoir of air or gas in excessof the capacity of that portion of the reservoir and communicating spaceabove the said point at which the said valve venting means opens fromthe reservoir, said venting means in-' cluding an additionalport andcoacting control edge therefor on the cylinder and plunger respectively.

l5. 'I'he'combination according to claim 14 in which the venting meansincluding an additional port and coacting control edge, therefor on 17.In a plunger pump for the pressure discharge of a predetermined butvariable quantity of fluid through a delivery outlet, a pump cylinder,8. plunger in the cylinder, a reservoir surrounding the cylinder, aninlet valve for the flow of fluid into the cylinder, a bypass valveforthe flowof fluid including any air or gas bubbles from tlie uppermost-part of the pump pressure space into the-reservoir on the deliverystroke after, the closing of the inlet valve, means for opening andclosing the said valves at' variable points relative to the stroke ofthe plunger, the

closing of the bypass valve controlling the beginning of dischargethrough the delivery outlet, and the inlet valve closing earlier as thebypass valve is closed earlier, whereby the quantity bypassed throughthe bypass valve is not reduced as the beginning 01' discharge is madeearlier, the reservoir having a resilient capacity expansible underpressure and being provided with valve means whereby on each deliverystroke of the plunger and. before the beginning of discharge, the fluidbypassed builds up a suitable pressure ,in the reservoir intermediate ofthe supply and discharge pressures, said pressure being maintained inthe reservoir during the period of discharge through the deliveryoutlet,

and a valve with controlling means therefor to relieve the pressure inthe reservoir and to vent the reservoir of air or gas in excess of adefinite quantity, at a suitable point in the stroke of the pump.

18. In a plunger pump having a delivery outlet for the high pressuredischarge of a part only of the volume of fluid displaced by the pump, areservoir for fluid under pressure forming part of the supply line tothe pump from a low pressure source of supply, said reservoir having a.resilient capacity expansible under pressure, inlet and bypass valvemeans between the pump pressure space and the reservoir, a part of thepump charge including any air or gas bubbles, being bypassed from thepump pressure space into the reservoir on the discharge stroke of thepump before the beginning of high pressure discharge through thedelivery outlet, and means whereby during a desired phase in the cycleof operation of the pump the reservoir is maintained at a suitablepressure stage intermediate of the supply and discharge pressures, saidmeans including a non-return valve in the supply line to the reservoir,and valve means opening at another phase in the cycle of operation ofthe pump for venting the reservoir of any air or gas bubbles separatingout from the fluid in the system and rising to the uppermost part of thereservoir, in excess of the capacity of that portion of the reservoirand communicating space above the point atwhich the valve venting meansopens from the reservoir.

19. A fluid pump according to claim 18, in which the reservoir ismaintained at a suitable pressure stage intermediate of the supply anddischarge pressures during the period in which the high pressure ofdischarge through the delivery outlet is developed, whereby the leakageof fluid at high pressure between the plunger and its cylinder isreduced by the reduced pressure differential on the inside and outsideof the cylinder walls.-

20. A fluid pump according to claim 18, 'in

which the valve means for venting the reservoir is opened at the end ofthe suction stroke of the pump, whereby the reservoir is maintained at asuitable pressure stage intermediate of the supply and dischargepressures during the suction stroke of the pump, and a more rapidfilling of the pump when the pressure in the reservoir exceeds a certainmaximum less than the pressure of discharge from the pump.

23. In a fluid pump in combination, a cylinder, a plunger cooperativetherewith as a pump for high pressure discharge of fluid from thecylinder through a delivery outlet provided with a loaded deliveryvalve, a closed fluid reservoir forming part of the supplyline to thepump from a low pressure source of supply, coacting ports and controledges therefor on the cylinder and u plunger respectively, including aninlet port and a bypass port, both adapted to provide a path of flowbetween the pump pressure space and the reservoir, the bypass portopening from that part of the pressure space which is uppermost at apoint higher than the inlet port and the said delivery outlet, wherebyfluid and any air or gas bubbles in the cylinder are bypassed out fromthe uppermost part thereof, into the reservoir, after the closing of theinlet port and before pressure discharge through the loaded deliveryvalve,

means for venting the reservoir at a point higher than the inlet andbypass ports open thereinto, to relieve the reservoir of air or gas inexcess of the capacity of that portion of the reservoir andcommunicating space above the said point at which the said valve ventingmeans opens from the reservoir, said venting means including anadditional port and coacting control edge therefor on the cylinder andplunger respectively, and

a non-return and safety valve in the supply line to the reservoir.

24. The combination according to claim 23 in which the venting meansincluding an additional port and coacting control edge therefor on thecylinder and plunger respectively, are'so. arranged and disposed thatthe reservoir is vented. when the plunger is at the end of itssuctionstroke.

25. The combination according to claim 23 in which the venting meansincluding an additional port and coacting control edge therefor on thecylinder and plunger respectively, are so arranged and disposed that thereservoir is vented when the plunger is at the end of its dischargestroke.

' ARTHURJFIELDEN.

